Heat a large sauté' pan over high heat with 3 Tbs. butter. When
hot, stir fry half of shrimp for 2-3 minutes. Remove from pan and repeat
with the rest of the shrimp. Deglaze pan with sherry until liquid has evaporated.
Add 1/2 stick butter, then sauté' onions and tarragon for about
2 minutes . Add flour and cook for 3 minutes. Add cream and chicken stock
granules, then cook for about 4 minutes or until mixture thickens. Whisk
in butter, 2 Tbs. at a time. Add mustard and salt and pepper to taste.
If sauce separates, re-whisk it briskly. Add shrimp and heat.